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Obama: 'We will get to the bottom of this"

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"We will find out who did this. We'll find out why they did this," Obama says

The president says he has ordered "full resources" of the federal government to respond

Obama pledges a full investigation

President Barack Obama said Monday he ordered the "full resources" of the federal government to respond to the Boston bombings on Monday, including increased security around the United States as necessary.

Pledging a full investigation to find out what happened, Obama said any individuals or groups responsible for what he called the "senseless" loss will "feel the full weight of justice."

The president spoke to reporters at the White House a few hours after explosions rocked an area near the finish line of Monday's Boston Marathon.

"I've directed the full resources of the federal government to help state and local authorities protect our people, increase security around the United States, as necessary, and investigate what happened," Obama said.

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Saying that "we still do not know who did this or why," Obama urged against jumping to conclusions in his statement that refrained from calling the explosions terrorism.

"But make no mistake: we will get to the bottom of this, and we will find out who did this," Obama said. "We'll find out why they did this. Any responsible individuals, any responsible groups, will feel the full weight of justice."

A White House official said after Obama spoke that "any event with multiple explosive devices as this appears to be is clearly an act of terror and will be approached as an act of terror."

"However, we don't yet know who carried out this attack and a thorough investigation will have to determine whether it was planned and carried out by a terrorist group foreign or domestic," the official said on condition of not being identified.